In order to enlarge and photograph a remote object to be photographed, a telephoto lens having a long focal length must be attached to a conventional lens interchangeable cameras which has been widely used. However, it is cumbersome for a user to carry and interchange lenses, so that a camera capable of selecting one of two focal lengths with simple operation has been developed recently.
A bifocal camear of this type incorporates two optical systems having different focal lengths inside the camera, and a user manually selects either of the two optical system before photographing. Although a selecting operation of the optical systems is simpler than conventional lens interchanging in such a bifocal camera, it takes a certain period of time. Therefore, a user may lose a good shutter chance when an object to be photographed is moved, and it is difficult to select a focal length while framing.
The present inventors have proposed a bifocal camera wherein a single optical system is commonly used and a motor is started upon operation of the button to move the main lens unit in the back-and-forth direction, and at the same time an auxiliary lens is inserted in or removed from an optical path, thereby automatically selecting a focal length (Japanese Patent Application No. 60-100381).
Most conventional collapsible lens barrels incorporated in a camera of this type having a main lens unit moved in the back-and-forth direction constitute a movable lens unit which is supported and guided by a linear guide member obtained by fixing a movable barrel to a camera body, and in which a lens unit attached thereto is moved in a direction of the optical axis.
This movable lens unit is located at different positions with respect to a camer a body in a collapsed (withdrawn) state and in an extended state. Since a large space is formed in front of a frame of the camera body in the extended state, external light tends to enter through a front body or an outer cover attached to the camera body and reach the film surface. Therefore, a light-shielding member must be provided between the movable lens unit and the frame.
In this light-shielding member, since light shielding must be maintained regardless of whether the movable lens unit is in the collapsed or extended state with respect to the camera body, a fixed light-shielding member cannot be used. For this reason, a bellows type light shielding member has been proposed in Japanese Utility Model Disclosure No. 59-68327.
However, it is difficult to manufacture the bellows itself in a mass production line, and the bellows has poor durability. In addiition, it is difficult to obtain a barrel unit because an opening at the back of the bellows must be connected to the camera body directly, thus presenting many manufacturing problems, e.g., low assembly efficiency.
Moreover, it is impossible to support or guide mechanical and electrical members for connecting the barrel with the camera body because the barrel itself is flexible, resulting in a big disadvantage in terms of a camera construction.